1. Field Of The Invention
This invention relates to optical digitizers, and more particularly to a system wherein the position of a probe or cursor in a coordinate system may be automatically digitized.
2. Description Of The Prior Art
It is frequently desirable to determine the location digitally of a cursor in a two or three coordinate system. Various techniques have been employed in the past for this purpose, employing various position sensing devices such as piezoelectric devices and magnetostrictive devices, or involving electromagnetic or electrostatic coupling of the cursor to an electrode array in a tablet. By the term "cursor" or "probe" used herein is meant an implement manipulated by a user or a machine over a surface or in space and whose position relative to the surface or space is to be determined and stored or displayed or whose position is to be set. While such arrangements have been in general satisfactory from the standpoint of the results that are achieved, they do have certain problems. For example, the boards or surfaces upon which the cursor is moved must be specially designed and are relatively expensive, thereby increasing the cost and reducing the portability of the system.
U.S. Pat. No. 4,568,182, issued to Modjallal and assigned to the assignee of the present application, discloses an optical system for determining the position of a probe or cursor which is movable on a plane surface having coordinate axes. The system includes a source of light which is rotated and thus scanned across a coordinate axes plane, and a detector receiving light from a reflector along certain angles to which the light beam is instantaneously directed. The coordinate system employs curved mirrors at the origin and at a point spaced from the origin along one of the coordinate axes, and plane mirrors extending along this coordinate axis. The light source is associated with the cursor. A calculator determines the position of the cursor in the coordinate system by triangulation. In another embodiment, the cursor is purely passive and includes a curved mirror, with rotating light sources and detectors positioned at determined points in the coordinate plane.